Krzysztof R. Apt is a Fellow at CWI (Centre Mathematics and Computer Science) in Amsterdam and Affiliated Professor at the University of Warsaw. He is also Professor Emeritus at the University of Amsterdam. He earned his Ph.D. degree in mathematics from the Polish Academy of Sciences in Warsaw in 1974. During his scientific career, he held tenure positions in Poland, France, the USA, and the Netherlands. Apt published four books and several articles in computer science, mathematical logic, and, more recently, theoretical economics. In computer science his research interests have included program correctness and semantics, use of logic as a programming language, design of programming languages, distributed computing, and algorithmic game theory. For the past 20 years he has been involved in a number of initiatives aiming at open access to scientific publications. He is a member of Academia Europaea, the founder and first Editor-in-Chief of the ACM Transactions on Computational Logic, and past president of the Association for Logic Programming. Together with Tony Hoare, he is the editor of this volume.